You can build a lever system and use a standard house scale. Here is an image that gives you and idea of how to do it, but if you search the web you'll find better directions. Replace trailer tongue with your car wheel and repeat four times. Add weight, you have total weight.
I used this method for my trailer weight, and, I used it once on the Miata before I got it corner weighted. It was accurate to within about 5% or so, roughly in both cases - this assuming that the scales used at the corner weighting place were 100% accurate, and I'm sure they are not.
R